1. Field of the Invention
This invention relates to methods and systems for sensing the presence or absence of liquid or gas around a sensor and, more particularly, for sensing and tracking the location of the wall of the cavity formed about a supercavitating vehicle and, even more particularly, to the sensing and identifying the location of the cavity wall relative to an underwater supercavitating vehicle without measuring the time-of-flight of an optical or RF signal.
2. Description of the Related Art
The U.S. Navy has funded long-running research programs for controlling supercavitating projectiles and vessels, referred to herein generically as supercavitating vehicles. Some of this work extends back to the 1940's and 1950's. The non-linear and high-speed nature of supercavitation makes control of supercavitating projectiles and vessels difficult.
Operating and controlling a supercavitating vehicle in an optimal manner involves limiting friction exerting drag on the vehicle. As is well known, a supercavitating vehicle operates within a cavity formed around the vehicle and contact between the supercavitational vehicle and the wall of the cavity increases the friction and thus the drag exerted on the vehicle. Thus, it is important to be able to extract and measure where the wall of the cavity is located, so that the vehicle can be operated in a manner that minimizes contact between the vehicle and the cavity wall. Stable guidance of the vehicle is critically dependent upon maintenance of the cavity so as to limit the friction exerted on the vehicle, and this guidance is dependent upon having quick and accurate information about the location of the cavity wall relative to the vehicle at all times. Thus, it is desirable to have a method for sensing and tracking the location of the cavity wall quickly and accurately.